Brewing coffee typically results in the extraction of 15% to 30% yield of dissolved solids from coffee particles, which are mixed with hot brew water for several minutes. A resulting fluid extract is gravity filtered from spent coffee grounds by a piece of filter paper. Commercial brewing machines provide about half a gallon of hot water, typically at about 195.degree. F. to a spray nozzle above a brew basket. In the brew basket is placed an open cup-shaped filter onto which is placed a quantity of flavor extractable coffee particles. When brew water is sprayed onto the loosely packed particles, the particles tend to float and many become suspended or fluidized in the brew water. This is believed to represent the ideal condition for brewing the maximum dissolved solids from the particles. Brew water is typically sprayed for about 3 minutes onto the particles where it continuously flushes extracted material from the particles as the fluid extract passes through the filter. The brew basket preferably has a discharge opening under the filter sufficient to drain all fluid extract from the filter in about 3 to 4 minutes.
A problem with the standard loose particle brewing system is that particle spillage and contamination are present at different points in the process. For example, particles may be spilled when manually dumping them into the cup-shaped filter. Also, particles may bypass the filter if brew water overflows the filter or the filter is otherwise placed improperly in the brew basket. Furthermore, each batch of spent grounds has to be removed and is often spilled when the wet filter is pulled from the brew basket for disposal. To solve the particle containment problem, the commercial brewing industry has adopted filter pouches of various designs, wherein a pre-measured quantity of loosely packed particles is totally enclosed within each pouch. The user therefore never handles particles directly.
Although filter pouches may solve one problem, they often cause other problems. For example, even though particles may be loosely packed within a filter pouch, insufficient space for particles to expand and become fluidized can result in the agglomeration of some particles. The agglomerated condition is much less conducive to extraction than is particle suspension. Lower percentages of dissolved solids are extracted when pouches have insufficient internal space. Prior art discloses pouches of complex and expensive construction which provide for pouch expansion in order to provide the required internal space.
Another pouch problem is that filter material located between the brew water spray and the pouch-contained particles may interfere with the fluidizing of particles. The brew water must first enter the pouch before particles may be fluidized for brewing. Although brew water easily passes through filter material, overall open area is often insufficient to allow the full flow of brew water into the pouch. If the pouch is not able to adopt a cup-shape to form a reservoir, some brew water may bypass the filter pouch, ultimately diluting the fluid extract from the pouch. Other pouch and brew basket designs intend for the pouch to form a fluid seal with the basket so that external bypass cannot occur. Such sealing is inconsistent, however. Furthermore, when a filter pouch is partially filled with particles in order to permit particle expansion, manual handling of the pouch may result in most of the particles accumulating at one end of the pouch. If this is not corrected when the pouch is manually laid horizontally in the brew basket, a portion of the pouch will likely be empty. Brew water easily finds such empty portions and flows directly through the pouch without contacting particles. This too is an undesirable form of brew water bypass.
What is needed is a filter pouch brewing system which reduces undesirable brew water bypass and yet provides sufficient space for particles to become suspended in brew water inside the pouch for consistently optimum brewing.